To add a child/family, you would go to the Family tab > Family List. From here click the Add Family button and enter in at least the required information (first name, last name, gender and birth date). Once you are done, click Save and it will prompt you to add in at least one guardian. Enter in at least the required information (first name, last name and relationship) and then click Save.

To add in additional guardians click the Add Guardian button in the Guardian section. Enter in at least the required information and click Save.

To add a contact, click the Add Contact button in the Contacts section. Enter in at least the required information and click Save.

Here's a quick tutorial video on how to add your first Family: